Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvii, 165 p.; also includes graphics (some col.). Includes bibliographical references (p. 158-165).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Vita. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 98-103). Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 297-303). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph.D.)--McMaster University, 2003. / Advisor: Natalia Georgieva. Includes bibliographical references. Also available via World Wide Web.

Thesis (M. Eng.)(Mechanical)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

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We test the controversial ideas about the role of corridors in fragmented animal habitats. Using simulation studies we analyze how fragmentation affects a simple prey-predator system and how the introduction of openings that connect the habitats changes the situation. Our individual based model consists of 3 levels: renewable prey food, as well as prey and predators that both have a simple economy. We find, in line with intuition, that the fragmentation of a habitat has a strong negative effect especially on the predator population. Connecting the fragmented habitats facilitates predator (and hence prey) survival, but also leads to an important counterintuitive effect: in the presence of a high quality predator, connected fragmented systems fare better in terms of coexistence than do unfragmented systems. Using a frequency domain analysis we explain how corridors between sub-habitats serve as "wave breakers" in the population flow, thus preventing deadly density waves to occur.

Terahertz (THz) reflection and transmission spectroscopy is a promising new field with applications in imaging and illicit material detection. One particularly useful application is for the detection of improvised explosive devices (IEDs) which is a favorite weapon of global terrorists. Explosive materials have been shown to have a unique spectral signature in the THz band which can be used to identify the explosives. However, the initial measurements performed on the explosive samples do not account for the modulation of the spectral features by random scattering that will be prevalent with actual samples encountered in applications. The intent of this work is to characterize and quantify the effects of random scattering that may alter the spectral features. Specifically, the effect that a randomly rough surface and granular scattering has on the scattered THz wave (T-Rays) will be investigated and characterized using the Finite-Difference Time-Domain (FDTD) simulation method. The FDTD method is a natural choice for this work as it can handle complicated geometries (i.e., multiple scatterers, arbitrarily rough interfaces, etc.) arbitrary materials (i.e., dispersive media, etc.) and provides broadband frequency data with one simulation pass. First, the effect that the randomly rough surface of the sample explosive has on the extracted spectral signature will be studied using a Monte-Carlo analysis. Then the effect of the complex structure inside the explosive material (the granular scatterers) will be considered. Next, when the physics of the rough surface and granular scattering are understood, a robust method to extract the spectral signature from the reflected T-rays will be developed.

Microwave circuits play an important role in wireless communications. Microwave circuits are made up of many components, including passive devices. Passive devices include resistors, capacitors, inductors, and transformers. These passive devices are used to help lower noise and to allow signals to pass effectively though the circuit. The Finite-Difference Time-Domain (FDTD) method is a powerful tool used to analyze the electromagnetic properties of objects. FDTD can be used to model the electromagnetic behavior of microwave circuits. Important electromagnetic properties such as S-parameters, effective dielectric constant, phase constant, and the movement of the electric and magnetic fields through the circuit can be extracted from a single FDTD simulation. Also of particular interest is the frequency response of a circuit, which can be determined by taking the Fourier transform of the time-domain results. FDTD is an efficient way to determine many electromagnetic characteristics of a microwave circuit. FDTD offers a programmer much freedom in assigning the shape, properties, and size of a structure that is to be analyzed. Also, FDTD is more robust than other electromagnetic analysis methods due to the algorithm it uses in finding the electric and magnetic fields. These useful aspects of FDTD make it the top choice in analyzing passive devices in microwave circuits. The thesis involves the electromagnetic analysis of passive structures that are used in RF IC's. Circuits that will be analyzed include a low-pass filter, antenna, and coplanar waveguides. This leads to the ultimate goal of the thesis, the analysis of a spiral inductor that is to be used in an RF IC. Spiral inductors are used as passive devices in planar microwave circuits. Spiral inductors can take on several shapes, with the square being the shape of interest in this thesis. FDTD will be used to analyze the electromagnetic properties of the spiral inductor, with the inductance being extracted from the values of the electromagnetic variables calculated during the simulation. Two types of spiral inductors will be analyzed; a three-turn spiral inductor and an eight-turn spiral inductor. Both types of spiral inductor will be analyzed on silicon and gallium arsenide dielectric substrates. The inductance values extracted from the spiral inductor can be used to determine how the inductor will behave as part of a microwave circuit. Inductor behavior is critical in that the performance of an RF IC will be affected if inductors are not performing optimally.